The present invention relates to a sheet feeding device wherein sheets stacked on a sheet stacking table are sucked to a suction surface by air to be fed out, and in particular, to an object wherein an air volume of floating air is made to be reasonable based on the state of floating in the case of blowing floating air against sheets stacked on the sheet stacking table.
An air sheet feeder has been used as a sheet feeding device of an image forming apparatus such as a copying machine. In the sheet feeding device, there is employed a mechanism wherein air is blown against a side edge surface of stacked sheets, and a sheet thus floated is sucked on a suction surface such as a perforated belt on which a suction opening that draws air is formed, and the belt is driven to rotate to convey the sheet.
With respect to the air sheet feeder of this kind, there has been proposed a technology in which an air volume is made to be variable depending on a sheet type (for example, see Unexamined Japanese Patent Application Publication No. 2005-75540). Further, there has been proposed a technology in which sheet feeding timing is detected to judge presence or absence of sheet feeding delay, and an air blowing operation is carried out (for example, see Unexamined Japanese Patent Application Publication No. 2005-96993).
In addition, there has been proposed a technology in which a period of time up to suction for sheet suction detection is measured to compare the measured time with a reference value, thus, the air volume is made to be variable (for example, see Unexamined Japanese Patent Application Publication No. S60-56739). There has further been proposed a technology to control an air volume by detecting a sheet floating position (for example, see Unexamined Japanese Patent Application Publication No. H07-89625).
In the technology described in Unexamined Japanese Patent Application Publication No. 2005-75540, it is impossible to cope with dispersion of the states in the same sheet type and with an influence of the state of keeping for sheets, because conditions are fixed by the sheet type. Further, in the technology described in Unexamined Japanese Patent Application Publication No. 2005-96993, it is impossible to judge whether floating of the sheet is appropriate or not, because a judgment is one under the state of sheet feeding. In the technologies described in Unexamined Japanese Patent Application Publication Nos. S60-56739 and H07-89625, a state is detected for the uppermost sheet among stacked sheets, and states of the second sheet and thereafter which are fed continuously are not reflected on the control of air volume.
Therefore, there have been generated dispersions on states of floating by air, and sure separation and conveyance of sheets have been impossible, resulting in problems.